In this section of our complete Monster Hunter World: Iceborne walkthrough, we are going to explain the process of the quest "A slimy secret". To obtain this optional mission, you will first have to face a Brachydios during the main story of the game via the mission "Punch operation (★★★)“. Then go talk to Seliana’s Sailor so that he asks you to capture this same creature (pictures1and2).
Fight the Brachydios in the Land of the Ancients until he ends up badly injured. Once a skull accompanies him on the world map, stop confronting him and simply follow him to his nest. When he goes to sleep, throw two tranquilizer bombs near him and then use one of your traps to capture him (picture3). By capturing a large monster, you will get more materials from it (picture4).
Once the free quest is completed, you will unlock new locations in the Botanical Conservatory as well as the special mission "Special Arena: Brachydios".